The rotary stencil printing device, well known as a stencil printing device, comprises a cylindrical, ink permeable printing drum which rotates around an axial line thereof with a stencil master plate wrapped around the outer circumferential surface thereof, printing ink being supplied from the inner circumferential surface of the printing drum, and a desired printing can be accomplished by pushing printing paper against the stencil master plate mounted on the outer circumferential surface of the rotating printing drum by using a press roller.
As an ink supply device for such a rotary stencil printing device, the applicant of the present invention previously proposed in Japanese patent application No. 2-37178 (Laid-Open Publication No. 3-240584) a squeegee blade type ink supply device which, by making use of a squeegee blade made of rubber-like elastic material engaging the inner circumferential surface of the printing drum at a certain squeegee angle, pushes and supplies printing ink from the inner circumferential surface of the printing drum by means of the squeegee blade which is stationary relative to the printing drum.
In such a stencil printing device, the printing drum normally consists of a cylinder having a circular cross section. In this case, since the inner circumferential surface of the printing drum is continuous over its entire circumference, the position of the squeegee blade relative to the inner circumferential surface of the printing drum is not substantially affected by the rotation of the printing drum, and the squeegee blade can be therefore fixedly secured.
However, in a stencil printing device using a cylindrical printing drum having a circular cross section, clamping means for the stencil master plate mounted on the outer circumference of the printing drum inevitably creates a large projection on the outer circumference, and the resulting large displacement of the press roller engaging therewith tends to cause an undesirably large impact accompanied by noises.
As another type of printing drum for a stencil printing device beside from the cylindrical printing drum having a circular cross section, there is known a printing drum having a non-circular cross section, or a D-type printing drum including an ink-permeable cylindrical part accounting for a major part of the entire circumference, and a non-concentric cylindrical part or a planar part accounting for a minor part of the entire circumference.
In a stencil printing device using a D-type printing drum, with the clamping means for the stencil master plate mounted on the non-concentric cylindrical part or the planar part of the printing drum, the projection on the outer circumference of the printing drum is generally decreased as compared to the case of a comparable cylindrical printing drum having a circular cross section, and the displacement of the press roller is accordingly reduced.
However, if the squeegee blade is fixedly secured, the squeegee blade is relatively more forcibly engaged by the non-concentric cylindrical part or the planar part of the printing drum, and this may adversely affect the supply of ink and the rotation of the printing drum.
To eliminate this problem and to prevent the excessive leakage of printing ink through the printing drum near the trailing edge of the stencil master plate, in Japanese patent application No. 02-37178 is proposed an ink supply device comprising a moveable structure for the squeegee blade in which the squeegee blade is forced away from the region corresponding to the non-concentric cylindrical part or the planar part of the printing drum. Patent applications corresponding to this Japanese patent application were filed in the United States, the United Kingdom, and Germany as U.S. patent application Ser. No. 07/654,105 (which has matured into U.S. Pat. No. 5,095,816), British Patent Application No. 9,103,387.8 (Publication No. 2,240,905), and P 41 05 292.7, respectively, and the contents of these patent application and the patent are incorporated herein by reference.
The excessive ink leakage at the trailing edge of the stencil master plate can be avoided if the squeegee blade is moved away from the inner circumferential surface of the printing drum in the region corresponding to the non-concentric cylindrical part or the planar part of the printing drum, but the ink reservoir which is developed in a triangular region defined by the squeegee blade and the inner circumferential surface of the printing drum behind the point of contact between the squeegee blade and the inner circumferential surface of the printing drum as seen in the rotational direction of the printing drum may be disrupted or disturbed to such a extent that the supply of ink which depends on the stable maintenance of the ink reservoir may be adversely affected.